Space-based surveillance systems use infrared detectors coupled to computerized data processors for monitoring heated objects and their movements in the atmosphere below and on the ground. The infrared spectrum covers a wide range of wavelengths, from about 0.75 micrometers to 1 millimeter. The function of infrared detectors is to respond to energy of a wavelength within some particular portion of the infrared region. Heated objects dissipate thermal energy having characteristic wavelengths within the infrared spectrum. Different levels of thermal energy, corresponding to different sources of heat, are characterized by the emission of signals within different portions of the infrared frequency spectrum. Detectors are selected in accordance with their sensitivity in the range of interest to the designer. Similarly, electronic circuitry that receives and processes the signals from the infrared detectors is also selected in view of the intended detection function.
Current infrared detection systems incorporate arrays of large numbers of discrete, highly sensitive detector elements the outputs of which are connected to sophisticated processing circuitry. By rapidly analyzing the pattern and sequence of detector element excitations, the processing circuitry can identify and monitor sources of infrared radiation. Though the theoretical performance of such systems is satisfactory for many applications, it is difficult to actually construct structures that mate a million or more detector elements and associated circuitry within a small area of about a square inch in a reliable and practical manner. Considerable difficulties are presented in aligning the detector elements with conductors on the connecting module and in isolating adjacent conductors in such a dense environment. Consequently, practical applications for contemporary infrared detection systems have necessitated that further advances be made in areas such as miniaturization of the detector array and accompanying circuitry, minimization of noise intermixed with the electrical signal generated by the detector elements, and improvements in the reliability and economical production of the detector array and accompanying circuitry.
Various constructions have been proposed to support the necessary connectivity and processing functions of the module. Those constructions have heretofore included the formation of a multi-layer passive substrate having metallized patterns formed thereon. Electronic devices such as integrated circuits are mounted on one or more of the substrate layers and connected to the metallized patterns to communicate signals between the electronic devices and the detector elements or external electronics. Conductive conduits formed upon opposite sides of each layer of such a multi-layer substrate are typically electrically interconnected by the use of conductive vias wherein a thin conductive film is sputter-coated into a through-hole interconnecting each side of the layer or substrate. Via interconnects with glass sealing plugs improve conductivity and enhance reliability of the conductive path. Glass sealing plugs also facilitate subsequent processing of the substrate wherein it is desirable to prevent fluid leakage from one side of the substrate to the other side thereof.
Some multi-layer module designs require a conduit to continue onto the edge of a substrate layer, for connection to adjacent modules or other external circuitry. Although "wrap around" connections have proven generally suitable for this purpose, they possess inherent deficiencies which detract from their overall effectiveness and desirability. The corner between the sides of the substrate is most susceptible to physical damage in subsequent processing and handling. In view of the shortcomings of wrap around connection, it is desirable to provide a more reliable electrical connection to conducting pads on the edges of substrate layers, using conventional integrated circuit manufacturing techniques.